Sender overload control



g- I. c. OSTEN-SACKEN ETAL 2,293,620

SENDER OVERLOAD CONTROL Filed NOV. 5, 1940 2 Sheets-Shet l ML MAME |.2,3.4.5. 5.7.9. QJOJI.

FIG.

7 1. c. 05 TEN-SAC/(EN V T '14. RAVNSFORD Aug. 18, 1942.

l. c. 'OSTENSACKEN ET AL SENDER OVERLOAD CONTROL Filed Nov. 5, 1940 2 Sheets-Sheet 2 6 NOV ATTORNEY Patented Aug. 18, 1942 UNITED STATES SENDER OVERLOAD CONTROL Irving 0. Osten-Sacken, Caldwell, and Arthur Raynsford, Bergenfield, N. J., assignors to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application November 5, 1940, Serial No. 364,342

9 Claims.

This invention relates to telephone systems and has for its object the reduction of delays due to peak traflic loads.

In designing telephone ofiices the amount of control equipment to be provided is based on handling ordinarily heavy traflic with a given small delay, so that there is practically no delay during the greater part of the time. On rare occasions an unusual rise in the number of calls originated at a particular oflice will occur, resulting in a shortage of control equipment which may persist for an appreciable length of time. Heretofore there has been no positive means for telling the subscriber of delay in cases of a shortage in control equipment.

In the panel system, the district selector is connected with a sender by means of a sender link including a sender selector. Normally, when the link is released this selector is left in the position last used, and, when the link is seized by the next call, may not be moved. If it is driven upward in search of an idle sender and reaches the top of its bank, it is returned to normal and continues to hunt until an idle sender is found. In the case of an all-senders-busy condition this search may continue until the subscriber hangs up. If the subscriber becomes impatient and dials prematurely, the sender when seized is not operated normally and a further delay results while the sender times out.

In accordance with the present invention, when an excessive sender load develops, a number of links are arranged to drive the district selector to an overflow position, if the sender selector hunts to the top of the bank.

The features of this invention will become more apparent from a consideration of the following description in connection with the drawings, in which:

Fig. 1 shows a district selector; and

Fig. 2 shows a link circuit.

These drawings are, in general, copies of Figs. 3 and 4 of U. S. Patent 1,944,269, granted January 23, 1934, to A. Raynsford et al. The circuits and apparatus embodying applicants invention will be found in the lower right corner of Fig. 2.

As set forth in the above-identified patent, a plurality of link circuits are arranged to serve groups of calling lines and are taken into service in rotation. When a link circuit completes its function, it hunts for and associates itself with a district selector which is ready for use and the link and district remain in a suballotted condition until the next link in the series has been put into service. The link circuit is then put into an allotted condition from which it will be advanced by the initiation of a call and the action of the start circuit.

It will be assumed that the link circuit of Fig. 2 has associated itself wtih the district selector of Fig. l and has been allotted and therefore sequence switch 300 is standing in position 2 and sequence switch 400 in position I. When the subscriber at substation I00 removes his receiver from the switchhook, the start circuit (not shown) will function to ground conductor 206, closing a circuit over the upper left and lower right contacts of cam 403, brush 402 and terminal 40!, conductor 318, upper right and lower left contacts of cam 30l, winding of relay 302 to battery.

Relay 302, in operating, closes a circuit from battery through the winding of up-drive magnet 304 of the line finder, right front contact of relay 302, lower right contact of cam 354, outer left front contact of relay 302 to ground at the lower left contact of cam 336. The line finder moves upward under the control of magnet 304, and with trip magnet 303 operated by the start circuit, the proper set of brushes is tripped. As soon as the line finder moves upward, a locking circuit is provided for relay 302 extending over its inner left front contact, upper contacts of cam 330, right back contact of relay 320, commutator strip 32!, brush 322 to ground, which holds relay 3G2 operated independent of the start circuit.

As soon as commutator brush 30! engages segment 305, a circuit is closed from ground over brush 301 and segment 305, lower right and upper left contacts of cam 306, to conductor 404. This circuit causes the release of trip magnet 303 and the restoration of the start circuit. When the line relay operated in responseto the initia tion of the call, battery was connected to conductor H4. Therefore, when line-finder brush 38| makes contact with terminal 300 which is connected to conductor I I4 and therefore to battery, a circuit is completed from this battery through the winding of relay 320, lower left and upper right contacts of cam 34!, to ground at the lower right contact of cam 339. Relay 320 operates in this circuit and closes a shunt around its winding through resistance -3l9-, to ground over commutator strip 32! and brush 322. The operation of relay 320 opens the locking circuit of relay 302, causing that relay to release. The release of relay 302 closes a circuit from ground through the winding of the cut-off relay (not shown), conductor H2, terminal 321, brush 326, inner left back contact of relay 3, right back contact of relay 302, lower left contact of cam 32 1, resistance 323 to battery. The operation of the cut-off relay opens the circuit of the line relay, removing battery from conductor H4, thus releasing relay 320.

At the time relay 332 operated as above described it closed a circuit in parallel to that for up-drive magnet 304 which may be traced as before from ground over the outer left front contact of relay 302, lower right contact of cam 3| l,

conductor 319, terminal 401, brush 466, over the bottom contacts of jack 481, right lower contact of cam 498, winding of relay 469, resistance 411 to battery. Relay 469 operates and closes a circuit from battery through the winding of sequence switch magnet 461], upper contacts of cams 412 and 496, to ground at the outer left contact of relay 469, advancing the link sequence switch 460 to position 2. With sequence switch 400 in position 2 a circuit is closed from ground over the upper right contact of cam 429, brush 418, terminal 411, conductor 315, lower right contacts of cams 312 and 313, left winding of relay 314 and battery. Relay 314 operates and locks over its outer left front contact to ground over the lower left and upper right contacts of cam 350. When relay 362 releases after the calling line has been found, a circuit is closed from battery through the winding of sequence switch 361], upper left contact of cam 328, right front contact of relay 314, left back contact of relay 3112 to ground at the lower left contact of cam 336. Sequence switch 360 advances to position 3 in this circuit, opening both the operating circuit and the locking circuit for relay 314.

When sequence switch 490 leaves position I, relay 409 is released. In position 2, a circuit is closed from battery through the winding of relay 413, upper contacts of cam 414, right back contact of relay 415, to ground at the lower right contact of cam 416. Relay 413 operates, closing a circuit from battery through the left winding of relay 411, left front contact of relay 413, to ground at the left back contact of relay 415. Relay 411, in operating, closes a circuit from battery through the winding of up-drive magnet 418 of the sender finder 421), left contact of cam 419, outer right contact of relay 411, to ground at the left back contact of relay 469. The sender finder moves upward under the control of magnet 418 in search of an idle sender.

Relay 413 also closes a circuit from battery through the right winding of relay 415, upper contacts of cam 421, left winding of relay 415, to

ground at the right contact of relay 413, while the test circuit extends from brush 422 over the lower contacts of cam 419, outer left back contact of relay 491, right back contact of relay 409, middle winding of relay 415, lower right and upper left contacts of cam 421, left winding of relay 415, to ground at the right contact of relay 413. An idle sender is characterized by battery connected to conductor 562. When, therefore, brush 422 engages terminal 423, corresponding to a sender which is assumed to be idle, the

test circuit above traced is completed over terminal 423 to battery and relay 415 operates quickly. The right-hand winding of relay 415 is wound difierentially with respect to the other two windings, so that if the test brushes of two links arrive on an idle terminal at the same time, either or both test relays may operate but will release as soon as either relay operates and shortcircuits its left-hand winding. Either or both links will keep on hunting, thereby preventing double connections. Relay 415 upon operating, short-circuits its left-hand winding, thereby closing low resistance ground to the test lead to the sender, as a temporary busy condition.

Relay 415 in operating closes a locking circuit for itself from battery from the sender over conductor 5112 and thenceas above traced through the middle winding of relay 415, lower right and upper left contacts of cam 421, to ground at the left front contact of relay 415. It also opens the circuit of relay 411 which releases, to in turn release magnet 418 and bring the sender finder to rest on the terminals of the idle sender. The release of relay 411 in turn releases relay 413. With relay 413 released and relay 415 operated, a circuit is closed from battery through the winding of sequence switch magnet 4116, lower left contact of cam 416, contact 421 of jack 428, left back contact of relay 413, right front contact of relay 415, to ground at the lower right contact of cam 416, advancing sequence switch 460 to position 3.

The further operation of the link circuit and the district selector in establishing a connection are not of interest in connection with the present invention and will not be described here, Reference may be made to the above-identified Raynsford et al. patent for a description of the omitted functions.

When the called line has been selected and the district selector is ready to be advanced to talking position, sequence switch 331] is in position 11 and sequence switch 430 in position 5. At this time ground is connected over the upper right contact of cam 336 to conductor 315, which is extended over terminal 433, brush 432, upper contacts of cam 446, middle winding of relay 415, right back contact of relay 469, left back contact of rela 491, left contact of cam 434, brush 431, terminal 430, to conductor 566.

After talking selections are completed, battery is connected to conductor 506. The current in this circuit is now sufiicient to operate relay 415 which closes a circuit from battery through the ,left winding of relay 411, left contacts of cam 421, to ground at the left front contact of relay 415. Relay 411 closes a circuit from battery through the winding of sequence switch magnet 490, upper contact of cam 419, outer right front contact of relay 411, left back contact of relay 439 to ground, advancing sequence switch 400 to position 6. In this position, all of the conductors extending to the sender are opened and the sender is completely released.

As soon as sequence switch 426 leaves position 5, relay 415 releases and in turn releases relay 411 unless the sender finder 426 is standing on one of its top ten terminals. If the latter is true, relay 411 is held operated in a circuit from battery over its left winding, left front contact, upper left contact of cam 424, commutator segment 464, brush 453 to ground. With relay 411 held operated at this time, a circuit is closed from battery through resistance 411, winding of relay 469, lower contacts of cam 414, inner right front contact of relay 411, lower right contact of cam 416 to ground. Relay 489 looks through its inner left contacts to ground at the lower contact of cam 461 and also closes a second locking circuit for relay 411. With relay 499 operated, a circuit is closed from battery through the winding of down-drive magnet 465 of the sender finder 426, left contact of cam 412, upper contact of cam 496, to ground at the outer left front contact of relay 409. When the sender finder reaches its lowermost position, a circuit is closed from ground over brush 463, bottom commutator segment 466, upper contact of cam 456 to resistance 411, shunting the winding of relay 469 and causing that relay to release and in turn release relay 411. With relay 411 released in position '6, a circuit is closed from battery through the winding of sequence switch magnet 430, lower right contact of cam 416, right back contact of relay 411 to ground at the lower right contact of cam 416, advancing sequence switch 430 to position 1.

During normal traffic, if the sender selector goes to the top of the bank, while hunting for an idle sender with sequence switch 400 in position 2, a circuit is closed from ground over brush 42%, commutator segment 492, upper left contact of cam 433, winding of relay 499 to battery through resistance 411. Relay 4119 operates and locks over cam 431 as above described. In addition, relay 439 closes a circuit from battery through the winding of down-drive magnet 465, normal contact of key 492, lower contact of cam 490 to ground at the outer left front contact of relay 439. The sender selector is restored to normal in this circuit. When brush 463 engages commutator segment 443 the circuit for shunting relay 439 is closed and relay 409 is released, opening the circuit of the downdrive magnet 485 and reclosing the circuit of the up-drive magnet.

Each sender as it becomes busy removes ground from an all-senders-busy circuit which controls an alarm. When this alarm sounds, key 493 may be'operated in any desired number of links. When the sender selector of a link in which key 493 is operated reaches the top of the bank in search for an idle sender with sequence switch 439 in position 2, the circuit of relay 499 is completed as previously traced. With key 493 operated a circuit is closed from ground over the outer left contact of relay 433, lower contact of cam 493, alternate contact of key 493, left winding of relay 491, brush 432, terminal 433, conductor 315, lower contacts of cam 313, to battery through the left winding of relay 311. Relay 311 being marginal does not operate but relay 431 operates and locks in a circuit from battery through its right winding and middle left front contact to ground over the lower left contact of cam 482.

At its left alternate contacts relay 491 connects ground to brush 492, completing a circuit over terminal 40!, conductor 318, upper left contact of cam 312, lower right contact of cam 313 to the left winding of relay 314 and battery. Relay 314 operates and looks over its outer left front contact and the lower left contact of earn 313 to its operating circuit.

With sequence switch 339 in position 3, the operation of relay 314 closes the previously traced circuit for sequence switch magnet 330, advancing the sequence switch to position 4. In this position a circuit is closed from battery through the winding of up-drive magnet 341 of the district selector, lower right and upper left contacts of cam 341, right front contact of relay 314, left back contact of relay 332 to ground at the lower left contact of cam 33%.

Since no sender is attached, the revertive pulses generated by the upward motion of the selector are ineffective to bring about the release of relay 354 and the selector continues to move upward until commutator brush 394 engages segment 395. When this occurs a circuit is closed from ground over the lower right contact of cam 339, brush 334, segment 395, upper right contact of cam 323 to the winding of magnet 393 and battery, advancing the sequence switch to position 1. The advance from position 4 deenergizes magnet 343, leaving the switch at the top of its bank.

In position 1, the circuit of relay EH4 is opened, but that relay reoperates in a local circuit from battery through its right winding, lower right contact of cam 396, upper left contact of cam 348, back contact of relay 320 to ground over commutator segment 321 and brush 322. With relay 314 reoperated, sequence switch 3110 is advanced to position 8. In this position the circuit for magnet 330 over commutator segment 395 is again closed and the sequence switch is ad vanced to position 11.

In position 11 a circuit is closed from a source of overflow tone 391, through condenser 398, left contacts of cam 339, right windings of repeating coil 36!), lower left and upper right contacts of cam 353, upper right contact of cam 312, lower left contact of cam 313, lower left and upper right contacts of cam 353 to ground. This tone is transmitted through the repeating coil to the calling telephone to inform the subscriber that the call cannot be completed. The release of the connection under the control of the calling subscriber takes place in the usual manner.

In the link circuit, the operation of relay 491 closes a circuit from ground over the middle right contact of relay 491 and the lower left contact of cam 41% to the winding of sequence switch magnet 433 to advance the sequence switch to position 3. Relay 4239 releases as soon as switch 44!! leaves position 2. In position 3, relay 491 closes a circuit over its outer right front contact, upper left contact of cam 4'19 to the winding of magnet 433, advancing the sequence switch to position 5, in which position a circuit is closed from battery through resistance 494, inner right contact of relay 491, middle winding of relay 415, upper contacts of earn 446, brush 432, terminal 433, conductor 315, to ground over the upper right contact of cam 336 as soon as sequence switch 339 has advanced to position 11.

At this time also a supplementary locking circuit is closed for relay 431 from battery through the right winding, middle and inner left contacts and left winding of relay 491 to brush 432 and ground as above traced, thus holdin the link until the district finder is moved.

Relay 415 operates in the above circuit and closes a circuit for relay 411 as previously described. Relay 411 looks to ground over the upper contact of earn 431 and advances sequence switch 439 to position 6 where relay 415 releases in turn releasing relay 411 and advancing the sequence switch to position 1. In this position the link circuit is ready to associate itself with another district selector. If another district is standing in position I, awaiting association with a link, a circuit will be closed from ground over the contacts which correspond to the lower left contact of cam 339 and contact 393 of jack 314 to conductor 392 and thence over contacts of jack 448, contacts of jack 449, upper contact of cam 415, right back contact of relay 415, upper contacts of cam 414 to the winding of relay 413 and battery. Relay 413 operates relay 411 which operates up-drive magnet 441 to move the district finder 410 in search of a district awaiting a link. As soon as brush 432 moves off terminal 433, relay 491 releases. The further restoration to normal of the link circuit is the same as described in the aboveidentified Raynsford patent.

Therefore, calls which are served by link circuits in which key 393 is operated, may be handled in the usual manner if the sender finder finds an idle sender on its first hunting operation. If not, and the sender finder reaches the top of its bank, the subscriber is given an overflow signal and the link is restored to normal. By this method enoughof-the incoming calls are dismissed quickly to relieve the peak load with the probable result that when the subscriber repeats his call he may be served without delay.

What is claimed is:

1. In a telephone system, telephone lines, selector switches, control equipment, link circuits for connecting said selector switches with said control equipment, means in said control equipment under the control or" a subscriber on one of said lines for operating said switching equipment to extend said line toward a second line for conversation, and manually controlled means in said link circuit for causing one of said selectors to advance to a position in which to transmit a busy signal to said calling subscriber.

2. In a telephone system, telephone lines, selector switches, control equipment, link circuits includin a pair of hunting switches for connecting said selector switches with said control equipment, means in said control equipment under the control of a subscriber on one of said lines for operating said switching equipment to extend said line toward a second line for conversation, and means responsive to a predetermined operation of one of said hunting switches for causing the connected selector to advance to a position in which to transmit a busy signal to-said calling subscriber.

3. In a telephone system, telephone lines, selector switches, control equipment, link circuits including a pair of hunting switches for connecting said selector switches with said control equipment, means in said control equipment under the control of a subscriber on one of said lines for operating said switching equipment to extend said line toward a second line for conversation, means responsive to a predetermined operation of one of said hunting switches, and manually controlled means to render said responsive means effective for causing the connected selector to advance to a position in which to transmit a busy signal to said calling subscriber.

4. In a telephone system, telephone lines, district selectors, a plurality of senders, link circuits each comprising a district finder and a sender finder for connecting one of said district selectors with one of said senders, means in said sender controlled by the subscriber on one of said lines for controlling said district selector to extend said line toward a called line, means in said link circuit normally efiective when said sender finder assumes a particular position during a hunting operation to restore said sender finder to normal and to advance said finder in a further hunting operation, and means to render said sender finder effective in said particular position to cause said district selector to advance to a position in which an overflow signal is transmitted to said calling subscriber.

5. In a telephone system, telephone lines, district selectors, a plurality of senders, link circuits each comprising a district finder and a sender finder for connecting one of said district selectors with one of said senders. means in said sender controlled by the subscriber on one of said lines for controlling said district selector to extend said line toward a called line, means in said link circuit normally effective when said sender finder assumes a particular position during a hunting operation to restore said sender finder to normal and to advance said finder in a further hunting operation, and manually operated means to render said sender finder efiective in said particular position to cause said district selector to advance to a position in which an overflow signal is transmitted to said calling subscriber.

6. In a telephone system, telephone lines, district selectors, a plurality of senders, link circuits each comprising a district finder and a sender finder for connecting one of said district selectors with one of said senders, means in said sender controlled by the subscriber on one of said lines for controlling said district selector to extend said line toward a called line, means in said link circuit normally efiective when said sender finder assumes a particular position during a hunting operation to restore said sender finder to normal and to advance said finder in a further hunting operation, and means to render said sender finder effective in said particular position to cause said district selector to advance to a position in which an overflow signal is transmitted to said calling subscriber and to cause the release of said link circuit.

7. In a telephone system, telephone lines, district selectors, a plurality of senders, link circuits each comprising a district finder and a sender finder for connecting one of said district selectors with one of said senders, means in said sender controlled by the subscriber on one of said lines for controlling said district selector to extend said line toward a called line, means in said link circuit normally eiiective when said sender finder assumes a particular position during a hunting operation to restore said sender finder to normal and to advance said finder in a further hunting operation. and manually operated means to render said sender finder eifective in said particular position to cause said district selector to advance to a position in which an overflow signal is transmitted to said calling subscriber and to cause the release of said link circuit.

8. In a telephone system, telephone lines, selector switches, control equipment, link circuits including a pair of hunting switches for connecting said selector switches with said control equipment, means in said control equipment under the control of a subscriber on one of said lines for operating said switching equipment to extend said line toward a second line for conversation, means normally effective to cause one of said hunting switches to perform a plurality of hunting operations in search of an idle control equipment and means to render said link circuit efiective, if no idle control equipment is found during a first hunting operation, for causing the connected selector to advance to a position in which to transmit a busy signal to said calling subscriber.

9. In a telephone system, telephone lines, district selectors, a plurality of senders, link circuits each comprising a district finder and a sender finder for connecting one of said district selectors with one of said senders, means in said sender controlled by the subscriber on one of said lines for controlling said district selector to extend said line toward a called line, means in said link circuit normally efiective to permit said sender finder to hunt for an idle sender in a plurality of stages and means to render said link circuit efiective if said sender finder fails to find an idle sender in the first hunting stage, to cause said district selector to advance to a position in which an overflow signal is transmitted to said calling subscriber and to cause the release of said link circuit.

IRVING C. OSTEN-SACKEN. ARTHUR RAY'NSFORD. 

